Tireless underwater robot is half fish, half jet plane

This robot fish doesn't get into a flap when it's time to go
for a swim. Instead, it glides to conserve energy, allowing it to gather water-quality data almost indefinitely.

When it's time for the fish to make more active manoeuvres, it
can swim by flapping its tail - but that would drain its battery in a few
hours. Most of the time, it uses a combination of pumping water out of its
body and rhythmically moving its battery to control its direction.

Grace, as the fish has been named, was designed and built by Xiaobo Tan of Michigan State
University in East Lansing.

Grace was taken for a test-drive in Michigan's Kalamazoo River,
where it detected crude
oil from a spill in 2010. That made it the first robotic fish
to demonstrate sampling with commercial water-quality sensors in a real-world
environment, says Tan.